Stupid question of the week: difference between K and L frame Smiths?

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rcmodel

April 15, 2009, 01:16 PM

The L has a larger frame window, to allow a larger cylinder diameter.
That makes the distance from the center pin to the bore longer.

This allows a full diameter barrel where it protrudes through the frame and cures the cracked forcing cone problem with the K-frame magnums. They had to have a flat milled off the bottom of the barrel to clear the cylinder gas ring which weakened them.

Also the top strap is slightly heavier on the L to resist flame cutting.

rc

GRIZ22

April 15, 2009, 01:19 PM

L frames are larger than K frames. Because of this they are stronger. L frames came out in the 80s so S&W would have a revolver smaller than a N frame (used for large 357s like the M27 and 41/44 maguns) capable of dealing with a steady diet of full power 357s. The K frame wouldn't handle full 357s for a long time and has issues with the forcing cone splitting with lightweight (110s and 125s) magnums.

Traditionally 38/357 caliber a J frame is always a 5 shot and K, L, and N frames a 6 shot, although there are 7 and 8 shot 357s made by S&W in L and N frame I believe.

Walkalong

April 15, 2009, 03:32 PM

K=Baby Bear, L=Mama Bear, N=Papa Bear....

Whatever frame the .500 is = Pro Wrestler....

First two posters got it for ya....Oh, and some L Frames are 5 shots..(.44 Spl goodness)

1KPerDay

April 15, 2009, 04:18 PM

So the model 19 is a K frame, right? Any problems with flame cutting on those?

The grip frames of the K and L are identical, right? (if what I read on the grip sites is correct....)

Thanks to all for the info.

rcmodel

April 15, 2009, 04:25 PM

Yes, the Model 19 is a K-frame.

Yes, if you shoot enough mag ammo, almost any revolver will exibit flame cutting to some extent.

It is not a deal breaker.

It slows down or stops after it gets so far.

The big issue with Model 19's was forcing cones cracking after a lot of 125 grain Magnum loads.

I have one I bought in 1970.
It is still going strong.

rc

dagger dog

April 15, 2009, 05:05 PM

Full length underlug on the barrel ala Python.

1KPerDay

April 15, 2009, 05:11 PM

never mind

bflobill_69

April 15, 2009, 05:16 PM

Hmm define ALOT of magnum ammo...

I have fired what I consider to be ALOT of magnum ammo through my 19 and she still performs exceptionally!

K Frames are tough... but if you KNOW you intend to shoot primarily .357, perhaps you should consider an L or N frame.

Bflobill69

rcmodel

April 15, 2009, 05:30 PM

Sorry, I can't define "a lot".
My 1970 19 has had what I consider a fair amount through it, with no problems. I shoot nothing but 140 grain JHP handloads at probably mid-level Magnum velocity.

My personal feeling is this:

Back in the day, cops shot a ton of LRN or LWC .38 Special ammo in practice.

Then they would switch to 125 grain JHP Magnum screamers to finish off the range session.
Without cleaning the leading out of the forcing cone first.

The packed on leading reduced the size of the forcing cone, and the 125 grain jacketed ammo made them big enough to go through, one way or another!

Cracked forcing cones were the result.

rc

Racinbob

April 15, 2009, 07:36 PM

Nice, rcmodel. Someone else realizes that. My 82 vintage with an uncountable number of rounds is still going strong.

harmonic

April 15, 2009, 08:00 PM

From my files:

The 125 grain bullets driven to maximum velocities used large charges of relatively slow-burning powders. Handloaders know the powder types as WW296 and H-110, among others. The combination of slow ball-type powders and the short bearing surface of the 125 bullets allows prolonged gas cutting of the forcing cone and top strap area, accelerating erosion and wear.

Borescope studies of rifle, machine gun, and auto cannon chamber throats shows a lizzard-skin-like texture due to this gas cutting damage, called "brinelling". The results of brinelling are fine microcracks that weaken the surface of the steel, and further promote erosion. In machine guns and auto cannons, barrel life is measured in terms of "useable accuracy", and round counts that determine this are based on group sizes at engagement ranges.

In the K-frame magnums, the forcing cone dimensions combined with the barrel shank dimensions results in a relatively thin shank at the 6 o'clock position, where a machine cut is made to clear the crane. This is usually where the forcing cone cracks. The L and N frames use much beefier barrel shanks and do not have this cut. S&W intended the K frame magnums to be "carried much and fired seldom" service arms, designed to fire .38 Specials indefinitely, with light to moderate use of .357 Magnums. You notice that S&W has discontinued production of K frame .357 magnums, no doubt due to product liability issues and a couple generations of K frame magnum experience.

tipoc

April 15, 2009, 09:08 PM

The problem with the K frames Magnums is often a bit overblown. There are a good many of these which have seen many thousands of rounds of 125 gr. loads which have never cracked nor seen much flame cutting beyond the norm.

The M19 was the first of the K frame Magnums and was introduced in the 1950s at the request of Bill Jordan who envisioned a lighter weight .357 than the N frames which were available. The concept was to make a strong daily carry gun for cops which was lighter and handier than the N frame. At that time common practice was for leos to practice with the lrn .38 Spl. and carry .357 on duty. The stated idea of the gun was a steady diet of .38 Spl., which the M19 handled rather easily, and limited use of the .357. The most common loading of the latter was with a 158 gr. lead bullet.

About the time the hotter jacketed 125 gr. loads showed up problems began to crop up with the forcing cones of the M19s. This was particularly true for guns where the lead from the .38s was allowed to build up in the area of the forcing cone. When the hot 125 gr. loads went through a gun with lead build up in this relatively weak area to begin with, the pressures rose much higher than normal and stressed this area, promoting cracks.

Last year Brian Pearce wrote an interesting article in Reloader magazine where he reported on his several years of shooting nothing but hot 125 gr. loads through an M19 and kept track of it. IIRC he was up to about 10,000 rounds or so. He'd had the gun tuned up a couple of times but no sign of a cracked cone.

There area good many decades old Combat Magnums around still strong and running. Keep them clean and properly tuned and the lead out, be mindful of what they were built for and they will last a good long time.

tipoc

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